A known cellular telecommunication system comprises at least a base station and a user equipment (UE). The base station and/or the user equipment are/is configured to use varying transmit power e.g. in order to reduce power consumption and to coordinate interference in the wireless network. As an example, cell range control techniques, mentioned further below, may cause the transmit power of a base station to vary. In some situations, this may lead to unforeseen problems.
The possibility of identifying user geographical location in wireless networks has enabled a large variety of commercial and non-commercial services, e.g., navigation assistance, social networking, location-aware advertising, and emergency calls. Different services may have different positioning accuracy requirements imposed by the application. In addition, some regulatory requirements on the positioning accuracy for basic emergency services exist in some countries, i.e. Federal Communications Commission (FCC) E911 in US.
Some known positioning methods rely on a database comprising information about cell areas. The information about cell areas is herein referred to as cell area description. Due to varying transmit power, the database may be corrupted and/or unreliable. As a result, the positioning methods may not provide a sufficiently accurate determination of a position of, for example, a user equipment.
In many environments, the position can be accurately estimated by using positioning methods based on GPS (Global Positioning System), which is, however, known to be associated with a cost due to a higher device complexity, longer measurement time, and more energy consumption. Nowadays networks have also often a possibility to assist UEs in order to improve the terminal receiver sensitivity and GPS startup performance (Assisted-GPS positioning, or A-GPS). GPS or A-GPS receivers, however, may not necessarily be available in all wireless terminals. Furthermore, GPS is known to often fail in indoor environments and urban canyons. There are complementary terrestrial positioning methods, e.g. Observed Time Difference of Arrival (OTDOA) in Long Term Evolution (LTE). Nevertheless, methods with lower accuracy such as those exploiting cell identities (Cell ID) or fingerprints are still of high importance and may become more important with dense wireless network deployments since the coverage area of low power radio nodes is typically small and the resulting positioning results may therefore be quite accurate and at the same time achievable at a very short response time. However, present positioning methods rely on that the transmit power of, for example, a low power node is constant. As mentioned in the foregoing, cell range control techniques, which are frequently employed for low power nodes, implies a varying transmit power. Thereby, present positioning methods become less accurate. Hence, there is a need for improvement.
Varying transmit power may result from for example cell range control.
Cell range control techniques according to prior art may be implemented by changing transmit power of a radio network node, such as an eNB or evolved-NodeB, or by changing cell selection offset at a receiver, such as a user equipment.
In the following, cell range control by changing the transmit power of a radio network node is explained. The maximum transmit power of a radio base station may vary in time per frequency carrier and Radio Access Technology (RAT) for various reasons, which results in non-uniquely defined areas describing the service area of a cell. Some of the examples are:                Energy saving operation of a radio node,        Transmit power restrictions for particular carrier frequencies and bands,        Power sharing among multiple RATs in a multi-RAT or multi-standard radio base station,        Power sharing among frequency carriers,        Power sharing among frequency bands,        Load balancing,        Capacity boosting during traffic-intensive hours and/or hotspot areas by turning ON some radio nodes or increasing power of some radio nodes, etc., and        Self Optimizing Network (SON) operation controlling cell coverage and coordinating interference in the network.        
In the simplest case, the maximum transmit power of a radio node may be defined statically. However, in practice, it may also be defined in a semi-static or dynamic manner. Furthermore, different power levels may apply on different physical signals (e.g. synchronization signals or reference signals) and different channels (e.g. traffic channels and broadcast channels).